The present invention relates to a sheet feeding apparatus used for a facsimile machine or a copy machine.
Facsimile machines and photocopiers generally have a sheet feeding unit to transfer sheets to a reading device incorporated in the facsimile machines and photocopiers so that the reading device can read an image on a sheet and convert it to an electric signal (i.e., image data). In order to perform a smooth reading operation to a large number of sheets, the sheets are usually plied up on a tray, and upon pressing of a read key, a roller unit of the facsimile machine or a copier contacts the pile of sheets and starts rotating to pick up the sheets one piece by one piece thereby transmitting them to the reading unit.
Generally, the reading unit has an upwardly directed reading unit to optically read the sheet. Therefore, the sheet should be fed to the reading unit with its upside down. Conventionally, the sheets are stacked on the tray with their upside down so that the sheets are taken from the bottom.
If the sheets are stacked on the tray with their upside up, a sheet feeding device picks up the sheets from the top of the pile on the tray. In this case, the sheets are turned upside down before they enter the reading unit. The facsimile machine or copier may have a U-turn passage or mechanism for this operation.
If the sheet feeding device has such a sheet turning mechanism, generally a sheet tray on a feeding side (referred to as "sheet feeding tray") is located above another sheet tray on a receiving side or a discharge side (referred to as "sheet receiving tray"). Therefore, the space required for these trays is small as compared with an arrangement in which the trays are situated in a coplanar manner. Further, since the sheets are piled on the sheet feeding tray with their upside up, an operator can see what is written on the sheet. This prevents errors in a copying operation and a sheet transmission. In addition, it is insured that a roller unit which picks up the sheets one piece by one piece functions properly regardless of the height (or weight) of the sheet pile on the sheet feeding tray. This is because the sheets are taken from the top of the pile. Specifically, if the sheet feed device takes the sheets from the bottom of the sheet pile, the roller unit may not function appropriately due to a large load exerted by the sheet pile.
The sheet feeding device which transmits the sheets from the bottom of the pile employs a separation roller unit and a separation pad to send the sheets piece by piece at one time. On the other hand, the sheet feeding device which transmits the sheets from the top of the pile generally has an arrangement for isolating one sheet from the sheet pile at each feeding operation as illustrated in FIG. 21 of the accompanying drawings. As shown in this drawing, the sheet pick up arrangement includes an isolation or separation roller Sr provided on a shaft A1 which positively rotates clockwise or in a sheet feeding direction, a retardation roller Rr provided on another shaft A2, which is located under the shaft A1 and positively rotates clockwise or in a direction opposite the sheet feeding direction, to contact the separation roller Sr with a certain force or pressure, an Am mounted on the shaft A1 to be swingable or pivotable about the shaft A1 upon operation of a solenoid (not shown), and a pick up roller Pr mounted on a free end of the arm Am and driven by the separation roller Sr via a gear or belt mechanism or the like. A torque limiter (not shown) is sandwiched interposed between the retardation roller Rr and the shaft A2.
A coil spring or the like (not shown) is also mounted on the free end of the arm Am to bias the arm Am upward. in a normal state, accordingly, the arm Am and the pick up roller Pr are forced to a raised position such that they do not become obstacles against a sheet loading operation onto a tray tr1. Further, friction between the sheets D and the retardation roller Rr is larger than a friction between the sheets D themselves in this arrangement.
Next, a sheet pick up operation will be described.
First, the solenoid is activated to rotate the arm Am clockwise or to move the same downward so that the pick up roller Pr contacts the top piece of the sheet pile D. Then, the pick up roller Pr rotates to feed the top sheet toward the separation roller Sr and the retardation roller Rr. At this point, the torque limiter does not allow a rotary power of the shaft A2 to be transmitted to the retardation roller Rr. Therefore, the retardation roller Rr is trailingly or dependently rotated by the separation roller Sr in an counterclockwise direction, as indicated by the outer counterclockwise arrow, whereas the shaft A2 rotates in the clockwise direction as indicated by the inner arrow. As the sheet reaches contact between the separation roller Sr and the retardation roller Rr, it is further transferred to another pair of rollers r1 and r2 located downstream in the sheet feeding direction by the separation roller Sr.
When the sheet reaches the transfer rollers r1 and r2, the solenoid is turned off and the arm Am swings upward due to the biasing force of the spring so that the pick up roller Pr leaves the sheets D to complete a separate and feed operation for one sheet. As this operation is repeated, the height of the sheet pile D becomes smaller. However, the pick up roller Pr can reach the sheet pile D of a reduced height as the arm Am is swung downward more. Therefore, it is possible to pick up all the sheets on the tray tr1 and transfer them to the separation roller Sr.
If more than one sheets are transmitted to the contact between the separation roller Sr and the retardation roller Rr, the bottom one of these sheets in touch with the retardation roller Rr is fed back to the tray tr1 by the rotary power of the retardation roller Rr which rotates clockwise in such a situation. Since the friction between the sheets themselves is weaker than that between the sheet and the retardation roller Rr, slippage occurs between the sheets and the rotary power of the separation roller Sr is not transmitted to the retardation roller Rr. As a result, the torque limiter acts to transmit the rotary power of the shaft A2 to the retardation roller Rr. Accordingly, only one sheet is allowed to pass through the separation roller Sr and the retardation roller Rr.
Referring to FIG. 22 of the accompanying drawings, illustrated is a conventional scanner portion of a facsimile machine which has a U-turn mechanism. In FIG. 22, A designates a main body of a scanner, B a U-turn guide member extending in a width direction (a right-and-left direction in the drawing) and C a cover. A sheet feeding tray tr1 is inserted into in entrance opening EN formed at an upper portion of the guide member B and sheets (not shown) are fed one piece by one piece to a transfer passage "m" through a feed roller "a" on the guide member B side and a separation roller "b" on the cover C side. Then, the sheets are U-turned by a second feed roller "d" located at a downstream end of the guide member B and a belt "e" located close to the second feed roller "d" and then transferred to a second transfer passage "f" on the main body A side. Thereafter, the sheets are read by a scanner (not shown) incorporated in the main body A. After a reading operation, the sheets are transferred by another pair of opposing transfer rollers "g" and "k", one located in the main body A and the other located in the guide member B, to an exit EX formed at a lower area of the guide member B and in turn to a sheet receiving tray tr2.
According to the conventional arrangement, the rollers "a", "d", "k" and other parts mounted on the guide member B are driven by a drive source (e.g., motor) M (not shown in FIG. 22; see FIG. 23), and the motor M is generally mounted on a bracket BK extending from one end of the guide member B. The motor M is therefore swingable together with the guide member B with a point (shaft) "i" being a pivot, as indicated by the broken line in FIG. 22. Thus, the guide member B and the motor M pivots over the main body A.
However, the conventional apparatus has the following problems:
i) since a solenoid is used to move the pick up roller Pr (FIG. 21) up and down, a cost is high, an electric control is needed and a structure becomes complicated. One object of the present invention is to eliminate this drawback, i.e., to provide a mechanical arrangement which can move a pick up roller inexpensively and easily and can realize a smooth and reliable sheet separation;
ii) if the sheet should be turned upside down in a sheet feeding device (FIG. 22), a relatively long transfer passage is required prior to the reading operation. Therefore, the width of the guide member B is inevitably elongated and the guide member B draws a large arc when it is pivoted to a stable open position as indicated by the broken arrow in FIG. 22 (the guide member B should be opened when jamming occurs). Consequently, a space for the arrangement becomes large. Another object of the present invention is to overcome this problem;
iii) a sufficient vertical step cannot be formed between the exit EX and the sheet receiving tray tr2 if a scanner unit placed in the main body A has a large width extending beneath the sheet receiving tray tr2 since the scanner unit limits the location of the tray tr2. If the width of the scanner unit was small, the tray tr2 could be located at a lower position. Still another object of the present invention is to eliminate this shortcoming. If a relatively large step is formed between the exit Ex and the tray tr2, the tray tr2 can hold a relatively large amount of sheets; and
iv) if the drive source M (FIG. 23) is attached to an end of the guide member B, a total width L of the sheet feeding device is enlarged. As a result, when the sheet feeding device is incorporated in a facsimile machine, a total width of the facsimile machine is also enlarged. Yet another object of the present invention is to provide a sheet feeding device which is compact having a relatively small width.
According to one aspect of the present invention, there is provided a sheet feeding arrangement which comprises a rotary shaft positively rotatable in a sheet feeding direction, a separation roller mounted on the rotary shaft, a retardation roller in contact with the separation roller with a certain force, an arm adapted to be able to move up and down relative to the rotary shaft, a pick up roller mounted on an end of the arm, and a rotary power transmission mechanism connected with the arm to transmit a rotary power of the rotary shaft to the pick up roller and to move the arm downward using the rotary power of the rotary shaft. The separation roller rotates as the rotary shaft rotates. The rotary power of the rotary shaft is transmitted to the pick up roller via the rotary power transmission mechanism. The rotary power of the rotary shaft causes the arm to move downward.
The separation roller may be provided with a one-way clutch to allow the separation roller to perform an idle rotation or a lost motion in a direction as the rotary shaft rotates (lost motion in the sheet feeding direction). If a peripheral velocity of a rotating transfer roller provided downstream of the separation roller in the sheet feeding direction is greater than a peripheral velocity of the rotating separation roller, the separation roller performs an idle rotation in the direction the rotary shaft rotates due to a friction between the sheet and the separation roller as long as the sheets are simultaneously contact the transfer roller and the separation roller. Therefore, the separation roller rotates at the same speed (peripheral speed) as the transfer roller.
The retardation roller may be connected with a drive source via a torque limiter and the drive source may drive the retardation roller in a direction opposite the sheet feeding direction (referred to as "reverse direction"). If more than one sheet are sandwiched by the separation roller and the retardation roller, the retardation roller rotates in the reverse direction. Thus, only one sheet is allowed to pass between the separation roller. If only one sheet exists between the separation roller and the retardation roller, which is an expected or desired situation, the retardation roller is disconnected from its drive source by the torque limiter while the separation roller is rotating in the sheet feeding direction. As a result, the retardation roller is driven by the separation roller and rotates in the sheet feeding direction to cooperatively work with the separation roller.
The arm may be biased upward by an elastic member. The arm moves upward due to a biasing force of the elastic member when the arm does not have to stay at a downward forced position.
The rotary power transmission mechanism may be elastically mounted on the arm and a torque generated by the elastic installation is larger than the biasing force exerted by the elastic member. Since the elastically generated torque of the rotary power transmission mechanism to the arm is greater than the biasing torque of the elastic member, the rotation of the rotary shaft causes the arm to move downward, but does not cause elements of the rotary power transmission mechanism to rotate. The rotary power is transferred to the pick up roller via the rotary power transmission mechanism upon completion of the downward movement of the arm.
A rotatable member for transmission of the rotary power to the rotary power transmission mechanism and the separation roller may be rotatable relative to the rotary shaft. A coil spring may be fixed to the rotary shaft at a one end thereof and to the separation roller at the other end and loosely fitted over the rotary shaft to form a spring clutch. As a diameter of the coil spring becomes smaller upon rotation of the rotary shaft, the coil spring and the rotatable member are tightly engaged (the coil spring clinches the rotatable member) to transmit the rotary power of the rotary shaft to the rotatable member (the rotatable member rotates and the rotary power transmission mechanism and the rotary shaft are connected with each other). If the transfer roller located downstream of the separation roller in the sheet feeding direction rotates faster than the separation roller in terms of peripheral speed, the separation roller rotates idly in the same direction as the rotary shaft due to a friction between the sheets and the separation roller as far as the sheet is forced to move by the transfer roller and the separation roller at the same time. Therefore, the separation roller rotates at the same peripheral speed as the transfer roller. This causes an idle rotation of the separation roller. As the separation roller performs the idle rotation relative to the rotary shaft, the diameter of the coil spring is enlarged since the other end of the coil spring which is fixed to the separation roller rotates and the diameter of the coil spring becomes greater and consequently the (tight) engagement between the coil spring and the rotatable member is released, whereby the rotary power of the rotary shaft is no longer transmitted the rotatable member.
According to another aspect of the present invention, there is provided a sheet feeding device of a type having a guide member pivotable about a shaft, sheets being U turned around the guide member prior to a sheet discharge operation, characterized in that a transversal section of the guide member is shaped to a configuration close to a circle, more specifically one having a semicircular lower half pivotably mounted on the shaft and a trapezoid upper half having a reduced free end. Since the guide member has a section similar to a circle, the width of the guide member can be designed relatively short (shorter than a prior art arrangement). Therefore, an arc movement of the guide member upon opening becomes smaller. It is also possible to form a sheet entrance opening and a sheet exit opening relatively closely in terms of vertical distance. This allows to form a relatively large step between the sheet exit opening and a sheet receiving tray.
A drive source for the rolls mounted on the guide member may be located inside the guide member. This reduces a whole width of the arrangement as compared with a prior art arrangement which has a drive source externally attached to the guide member.